ORIGINAL: JPMacG
I have noticed that some engines don't run well with larger tanks. I don't know why, maybe it's something to do with pressurization from the muffler.
This has been my experience also. My Magnum 15 used a 4oz tank, I switched to 3oz and it ran better from full to empty.
On the other hand, my Saito 45 will run 35 minutes on an 8oz tank without a hitch. The 45 was replaced with an 82, 8oz is the perfect size. I used to like a flight lasting 20-30 minutes, 10-12 is more enjoyable for me now.